This invention relates to a method of removing an acid halide, anhydride, or ester from a mixture with a compound with which it codistills. In particular, it relates to reacting the acid halide, anhydride, or ester with an amine to form a higher or lower boiling compound, followed by distillation.
Parachlorobenzonitrile (PCBN) can be used to make pigments, pharmaceuticals, and agricultural products. It is made by reacting parachlorobenzoic acid with parachlorobenzotrichloride (PCBTC) and ammonium chloride (see U.S. Pat. No. 5,866,709, herein incorporated by reference). In making PCBN, various side products and unreacted starting material can end up in the product mixture. Most of these impurities can be separated by distillation, but the boiling point of one side product, parachlorobenzoyl chloride (PCBOC), is only 2.degree. C. less than the boiling point of PCBN(223.degree. C.),so it codistills with the PCBN. The presence of PCBOC in the PCBN is not acceptable to some users of PCBN as it lowers the quality of the products made from PCBN. While separation could be accomplished by crystallation or further distillation, those processes are not cost effective.